The proposed research is aimed at studying molecules of biological and pharmacological interest, with the purpose of obtaining correlations between electron distribution and chemical or biological parameters. Nitrogen atoms generally play an important role in molecules of biological, biochemical, and pharmacological importance, so that knowledge of the electronic environment of nitrogen atoms can be of great use in determining the properties of these molecules. Since the nitrogen-14 nuclear quadrupole resonance (NQR) frequencies are sensitive to the electric field gradients at the nitrogen-14 nucleus, NQR spectroscopy is ideal for probing this electronic environment. From the observed NQR frequencies one obtains values for the quadrupole coupling constants and asymmetry parameters of the nitrogen atoms in the molecules of interest. These two parameters can be related to the sigma and pi electron densities at the nitrogen sites. Correlations might then be found between these charge densities and the Hammett sigma constants, certain measures of biological activity, and other properties. The charge densities can also be used to determine the tautomeric structures of the compounds of interest.